Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
  • G01T1/2914—Measurement of spatial distribution of radiation
  • G01T1/2985—In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis)
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
  • A61B6/03—Computed tomography [CT]
  • A61B6/032—Transmission computed tomography [CT]
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/40—Arrangements for generating radiation specially adapted for radiation diagnosis
  • A61B6/4007—Arrangements for generating radiation specially adapted for radiation diagnosis characterised by using a plurality of source units
  • A61B6/4014—Arrangements for generating radiation specially adapted for radiation diagnosis characterised by using a plurality of source units arranged in multiple source-detector units
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/161—Applications in the field of nuclear medicine, e.g. in vivo counting
  • G01T1/164—Scintigraphy
  • G01T1/1641—Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras
  • G01T1/1647—Processing of scintigraphic data
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
  • A61B6/027—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral

Definitions

• the present application relates to medical imaging systems. It finds particular application to computed tomography (CT) and, more particularly to stereo tube CT imaging techniques.
• CT computed tomography
• An exemplary CT system may include an x-ray tube mounted on a gantry opposite one or more detectors. During scanning, the x-ray tube emits radiation that traverses an imaging region and strikes the one or more detectors, which generate signals indicative of the detected radiation. The resulting signals are reconstructed to generate volumetric data, which is used to produce one or more images of a scanned region of a subject residing within the imaging region.
• Axial scan protocols can be used with such systems to serially capture finite regions or slices of the subject.
• the width of the detector limits the width of the region of the subject that can be imaged during each scan. This may be coverage prohibitive, for example, when desiring to capture a part of a structure or a whole structure that is larger than the detector width.
• a helical (or spiral) scan can be performed. With helical scans, the subject may be continuously moved through the imaging region via a mobile support or couch while the x-ray tube rotates around the imaging region and data is collected. The resulting data may be representative of structure with a size that exceeds the width of the detector(s).
• helical data acquisitions may take more time than axial data acquisitions due to couch ramp up delays, multiple x-ray source revolutions, etc.
• an axial scan protocol may not provide the coverage to acquire the desired volume of interest in a single axial scan.
• a helical scan protocol may provide the desired coverage, however, at the cost of time.
• temporal resolution may decrease and motion artifact may increase relative to an axial scan.
• Cone beam CT systems using one or more large area detectors allow scanning of relatively larger volumes of anatomy (e.g., whole organs) with axial scan protocols.
• the data acquisition is limited in that conventional axial cone beam CT scanning techniques fail to provide complete sampling.
• the images generated from such data may include inherent artifacts such as streaking.
• the deficiency in data can be theoretically or mathematically determined and mitigated by using two x-ray sources in a stereo tube configuration and combining the detected data.
• a stereo tube configuration at least two x-ray sources are positioned at the same angular position along different z-axis locations and share a common detector(s) for data acquisition. Since the detector(s) is shared, the x-ray sources have been sequentially (alternately) switched "on” and "off such that radiation from only one of the x-ray sources illuminates the shared detector(s) at any given time.
• both of the x-ray sources move out of the image plane during some portion of the axial scan.
• a data set with enough data for reconstruction with a traditional cone beam CT reconstruction algorithm can be generated. This data set can be reconstructed and used for generating one or more images.
• the power may have to be increased (e.g., doubled) to achieve a photon flux and signal-to-noise ratio (SNR) similar to that of a system with a continuously "on" x-ray source, and this may not be feasible since conventional x-ray sources generally are power limited.
• x-ray sources driven in a sequential mode typically cannot be switched completely “off such that no radiation is emitted.
• residual photon flux from the "off x-ray source may contaminate the signal of the "on" x-ray source.
• afterglow of the detector(s) may have a relatively greater effect since temporal cross-talk of the different x-ray sources can be relatively stronger.
• a computed tomography system includes at least two x-ray sources, at least one common detector, and a reconstruction system.
• the at least two x-ray sources are aligned at different z-axis locations at about a same angular position and concurrently emit radiation that traverses an imaging region.
• the at least one common detector detects radiation emitted by the at least two x-ray source and generates composite data indicative of the detected radiation.
• the reconstruction system reconstructs the composite data to generate one or more images.
• a computed tomography method includes concurrently emitting radiation by at least two x-ray sources positioned at different z-axis locations at about a same angular position around an imaging region that traverses the imaging region, detecting the radiation from the at least two x-ray sources with at least one common detector, generating composite data indicative of the detected radiation, and reconstructing the composite data to form an image.
• a computed tomography imaging system includes a means for concurrently emitting radiation by at least two x-ray sources aligned in a stereo tube configuration, a means for concurrently detecting the radiation from the at least two x-ray sources, a means for generating a signal indicative the detected radiation from the at least two x-ray sources, and a means for reconstructing the signal having contributions from both of the least two x-ray sources to generate an image.
• the invention may take form in various components and arrangements of components, and in various steps and arrangements of steps.
• the drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.
• FIGURE 1 illustrates a multi-source medical imaging system that employs concurrently emitting x-rays sources arranged in a stereo tube configuration.
• FIGURE 2 illustrates an exemplary method for imaging with a multi-source medical imaging system that employs concurrently emitting x-rays sources arranged in a stereo tube configuration.
• FIGURE 3 illustrates two x-ray sources in a stereo tube configuration emitting beams that overlap and strike a common detector.
• FIGURE 4 illustrates an exemplary iterative reconstruction technique.
• a medical imaging system 100 includes a scanner 104 having N x-ray sources 108i, 108 N (collectively referred to herein as x-ray sources 108), wherein N is an integer greater than one.
• the x-ray sources 108 can be used to generate a cone beam, a fan beam, or other beam geometries.
• each of the x- ray sources 108 can produce and emit radiation having a similar or different spectral distribution, intensity, and/or other characteristics.
• the x-ray sources 108 reside at about a same angular position about an imaging region 112 and are offset along a z-axis 116. It is to be appreciated that in another embodiment the at least two of the x-ray sources 108 can be positioned at different angular positions and offset along the z-axis 116. In yet another embodiment, the at least two of the x-ray sources 112 can be positioned at different angular positions and at about the same location on the z-axis 116.
• the x-ray sources 108 are disposed about a rotating gantry 120. In such instance, rotating the gantry 120 about the imaging region 112 rotates the x- ray sources 108 about the imaging region 112. It is to be appreciated that such x-ray sources 108 may originate within separate x-ray tubes that are physically attached to the gantry 120. Such x-ray tubes can be positioned as described above, for example, such that the x-ray sources 108 are at about the same angular position and offset along the z-axis 116. Conventional beam controlling electronics can be used to accurately control the x-ray sources 108 to compensate for any differences in relative physical position with respect to the angular positioning of the x-ray tubes.
• the x-ray sources 108 can originate from different foci within the same tube. Likewise, this tube can be physically attached to the gantry 120 and the radiation emitted from each of the foci can be controlled accordingly by electronics to accurately position the x-ray sources 108.
• the system 112 may have a combination of tubes in which one or more have a single one of the x-ray sources 108 and one or more have multiple ones of the x-ray sources 108.
• the x-ray sources 108 are generated by a device(s) separate from the gantry 120. For instance, the x-ray sources 108 can be produced from an electron beam generator or gun that controls the position of an e-beam through electronic deflection or the like.
• the scanner 104 further includes one or more detectors 124 ("detectors 124"), wherein each of the detectors 124 have at least one detector element. It is to be appreciated that each of the detectors 124 may be different or similar in dimension, energy resolution, shape, etc. In one instance, at least one of the detectors 124 is a large area detector. As such, the detectors 124 may include two-dimensional detectors with two or more detector elements. Using such detectors 124 enables larger volumes, widths, regions of interest or the like within a subject to be scanned using axial scan protocols relative to one-dimensional detectors.
• Such scanning capabilities can be leveraged to quickly acquire data representative of larger areas or whole organs in a single axial scan. This facilitates acquiring relatively high temporal resolution data with relatively broad coverage, if desired.
• scanning can be used in connection with functional imaging such as perfusion imaging in which a contrast(s) or other agent(s) quickly moves through tissue of interest, metabolic imaging, and the like.
• Each of the detectors 124 may be based on different or similar detector technologies.
• suitable technologies include, but are not limited to, indirect conversion technology (e.g., incorporating a gadolinium oxysulphide (GOS) scintillator), direct conversion technology (e.g., incorporating crystalline cadmium zinc telluride (CZT)) material), or other technologies.
• indirect conversion technology e.g., incorporating a gadolinium oxysulphide (GOS) scintillator
• direct conversion technology e.g., incorporating crystalline cadmium zinc telluride (CZT) material
• CZT crystalline cadmium zinc telluride
• the detectors 124 subtend an angular arc opposite the x-ray sources 108, and the imaging region 112 is defined therebetween.
• each of the detectors 124 rotates along with the x-ray sources 108, for example, as with a third generation CT system.
• the detectors 124 reside at a static angular location about a stationary gantry.
• the detectors 124 detected radiation at any moment in time are determined by the angular position of the x-ray sources 108, for example, as with a fourth generation CT system.
• the detectors 124 detect radiation emitted by the x-ray sources 108. Anti- scatter grids or the like can be used to reduce the detection of scatter radiation.
• a support 128 supports a subject, such as a human, within the imaging region 112.
• the support 128 may be movable in order to guide the subject to a suitable location within the imaging region 112 before, during and/or after performing a helical, axial, and/or other scan, for example, by moving the support 128 along the z-axis 116 and/or one or more other axes.
• a control component 132 controls each of the x-ray sources 108. Such control includes, but is not limited to, activating the x-ray sources 108 to emit radiation during scanning and deactivating the x-ray sources 108 to terminate such emission.
• control component 132 controls the x-ray sources 108 such that at least two of the x-ray sources 108 concurrently emit radiation during data acquisition.
• the concurrently emitting x-ray sources 108 typically are driven with about the same power, for example, each can be driven with the same power used in systems with a single continuously emitting x-ray source.
• each of the x-ray sources 108 Since each of the x-ray sources 108 is continuously driven to emit radiation, the peak power of the photon flux and the signal-to-noise ratio (SNR) for each of the x-ray sources 108 is as if it were the only x-ray source emitting radiation.
• the x-ray sources typically are alternately activated, which can result in a reduction of photon flux and increased noise at the same power level.
• grid switches, gates, shutters, and the like are not needed to switch the x-ray sources 108 "on" and "off during data acquisition when it is not necessary to switch the x-ray sources 108.
• such components can be implemented when needed or desired.
• temporal resolution can be increased relative alternately operating the sources since more data is obtained in about the same amount of time.
• each of the detectors 124 concurrently detects radiation emitted by more than one of the x-ray sources 108. Since the x-ray sources 108 are located at different locations along the z-axis 116, the radiation emitted thereby travels through different paths through the imaging region 116 and represents different information.
• FIGURE 3 wherein x-ray sources 304 and 308 are positioned at different positions along a z-axis 312. A beam 316 emitted by the x-ray source 304 is collimated by collimators 320 and illuminates a portion of a common detector 324.
• a beam 328 emitted by the x-ray source 308 is collimated by collimators 332 and illuminates a portion of the common detector 324. As depicted, the beams 304 and 308 overlap on the common detector 324.
• the dynamic range of the detectors 124 can be suitably configured by conventional techniques based on the number of x-ray sources 108 concurrently emitting radiation since each x-ray source 108 contributes to the x-ray intensity seen by the detectors 124.
• each of the detectors 124 Upon detecting radiation from the x-ray sources 108, each of the detectors 124 generates a signal indicative of the detected radiation. Since radiation from multiple x- ray sources 108 is concurrently detected, the generated signals have contributions or components corresponding to each of the emitting x-ray sources 108.
• Such signals are provided to a reconstruction system 136 for reconstruction of volumetric data indicative of the object.
• the reconstruction system 136 has a multi-source reconstructor 140 that takes into account that each signal from the signal corresponding to the overlapping position of the detectors 124 is a composite signal with contributions from each of the N x-ray sources 108.
• the reconstructor 140 can be hardware or software.
• the reconstructor 140 includes a computer processor that executes computer readable instructions stored on computer readable medium.
• An image processor 144 processes the reconstructed data to generate one or more images.
• the generated images can be displayed, filmed, archived, forwarded to a treating clinician (e.g., emailed, etc.), fused with images from other imaging modalities, further processed (e.g., via measurement and/or visualization utilities and/or a dedicated visualization system), stored, etc.
• a computing system (or console) 148 facilitates operator interaction with and/or control of the scanner 104.
• Software applications executed by the computing system 148 allow the operator to configure and/or control operation of the scanner 104. For instance, the operator can interact with the computing system 148 to select scan protocols, initiate, pause and terminate scanning, view images, manipulating volumetric image data, measure various characteristics of the data (e.g., CT number, noise, etc.), etc.
• the computing system 148 also communicates various information to the control component 132.
• FIGURE 4 illustrates an exemplary reconstruction approach 400 employed by the reconstructor 140.
• the system 100 can be modeled as a function of the N x-ray sources 108. In one instance, this is achieved by solving for the unknown attenuation coefficients in the attenuation map. For example, the unknown attenuation coefficients can be described and solved for in terms of line integrals or otherwise.
• the resulting function is a summation over the N x-ray sources 108 and accounts for arbitrary overlap of the x-ray beams on each of the detectors 124. This model can be used in connection with the following iterative reconstruction approach.
• an initial image estimate for a stereo tube CT system simultaneously emitting radiation is generated.
• the image estimate is forward projected to generate projection data.
• the forward projection data is compared with an objective function.
• the objective function is a log-likelihood of the above system model, which considers signals corresponding to multiple beam overlap.
• this comparison is used to adjust the image estimate.
• Various known techniques can be used to maximize the function to increase the likelihood with each iteration. For instance, an expectation-maximization approach can be used to monotonically increase the likelihood.
• Other suitable techniques include, but are not limited to, coordinated ascent, ordered subset, and paraboloidal approaches.
• a maximum likelihood function is used to sequentially update voxels during each iteration based on the N x-ray source contributions.
• the multi-source reconstructor 140 forward projects data for each of the N x-ray sources 108 each iteration.
• the forward projected data is adjusted and allocated to each of the N x-ray sources 108. This can be achieved through computing a difference between an aggregate of the forward projected data and the measured data and scaling the forward projected data based on this difference.
• the data is then backprojected for each source as a weighted function of the x-ray source contribution to the aggregate contribution. This accounts for the N x-ray sources 108.
• Each iteration is completed upon sequentially updating the voxels, and with each iteration, the allocation of the data updates and converges.
• This process of forward projecting the estimated image, comparing the forward projected data to the objection function, and updating the estimated image continues until a desired level of agreement with the forward projected data is reached.
• FIGURE 2 illustrates a non-limiting method 200 for concurrently using at least two x-ray sources 108 in a stereo tube configuration to image a subject. Similar to the system 100, the x-ray sources 108 can be paired with the detectors 124 in a third, fourth, or other generation systems.
• SPECT single photon emission tomography
• the x-ray sources 108 can be positioned such that they are at about a same angular position about the imaging region 112 and offset along the z-axis 116.
• the x-ray sources 108 may be attached to and rotate with the rotating gantry 120.
• At reference numeral 204 at least two x-ray sources 108 concurrently generate and emit radiation through the imaging region 112. Such radiation can be cone beam, fan beam, or beams with other geometries.
• each of the x-ray sources 108 can emit radiation of similar or different spectral distribution, intensity, and/or other characteristics.
• the radiation from each of the x-ray sources 108 traverses the imaging region 112. Since the x-ray sources 108 reside at different z-axis locations, the radiation emitted by each of the x-ray sources 108 traverses a different path through the imaging region 116.
• each of the detectors 124 may have one or more detector elements.
• the detectors or detector elements therein may be of different or similar dimension, energy resolution, shape, etc.
• the detectors 124 are large area two-dimensional detectors that can be used to detect data corresponding to multiple slices, larger volumes, widths or regions of interest, etc. relative to one- dimensional detectors. Such detectors 124 can be used to acquire data corresponding to larger areas or whole organs in one axial scan.
• each of the detectors 124 generates a signal indicative of the detected radiation.
• the generated signals have radiation contributions from each of the emitting x-ray sources 108.
• these signals are provided to a reconstruction system 136, which reconstructs the signals using various reconstruction techniques to produce volumetric data indicative of the scanned region of the subject.
• the reconstruction system 136 uses the reconstructor 140 to reconstruct the signals.
• the volumetric data is processed to generate one or more images that can be displayed, filmed, archived, fused, or otherwise processed.
• CT computed tomography
• Such applications include cardiac CT in which it is often desired to image the whole or a substantial portion of the heart relatively quickly to improve temporal resolution.
• Examples of other applications include perfusion scans, functional scans, metabolic scans, and the like.

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• 2007
  • 2007-07-23 WO PCT/US2007/074091 patent/WO2008021661A2/en not_active Ceased
  • 2007-07-23 EP EP07840471.2A patent/EP2049918B1/en not_active Not-in-force
  • 2007-07-23 CN CN2007800284694A patent/CN101495886B/zh not_active Expired - Fee Related
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